1. Field of the Invention
The present invention relates generally to tire pressure monitoring systems and more particularly, to such a tire pressure monitoring system, which utilizes a wireless transmission technique and a wired transmission technique to transmit detected data to a monitoring unit.
2. Description of the Related Art
A wireless tire pressure monitoring system outputs measured tire pressure data from each vehicle wheel in the form of a packet by means of a radio frequency. The packet envelops measured pressure data of every vehicle wheel and the corresponding identification code. When a receiving antenna in the chassis or the inside of the vehicle received the RF signal of the packet, the package is read through RF circuit processing for enabling the monitoring main unit in the driver's cab to display the tire pressure of every vehicle wheel. More particularly, the use of a wireless tire pressure monitoring system in a towing vehicle or the like where the wheels operate under a high load condition can effectively monitor the tire pressure status of every wheel, thereby maintaining the service life of the wheels and assuring driving safety. However, following population of wireless communication applications, the overlap condition of RF bandwidth is frequently seen. Digital transmission utilizes a specific packet verification technique to discriminate wireless communication signals. However, processing of external RF signals within the same bandwidth relatively increases the bit error rate and the chance of packet collision.
FIG. 5 illustrates the arrangement of a wireless tire pressure monitoring system 1 in a towing vehicle 2 according to the prior art. As illustrated, the monitoring main unit 10 in the driver's cab at the truck-tractor 21 is electrically connected to a receiving antenna 12 at the bottom side of the chassis of the towing vehicle 2 through a transmission line 11, and a tire pressure sensor 13 is installed in each wheel 23 of the truck-tractor 21 and each wheel 24 of the platform (or trailer) 22. Each tire pressure sensor 13 sends the measured data in the form of a packet to the receiving antenna 12 by means of a radio frequency. According to this design, the receiving antenna 12 receives the RF signals from all the tire pressure sensors 13. By means of the use of a high-power transmitting antenna, the tire pressure sensor 13 that is disposed far away from the receiving antenna 12 can effectively send the signal to the area within the effective receiving range of the receiving antenna 12. For the sake of one single specification for convenient use, all the tire pressure sensors 13 must use a same high-power transmitting antenna. Further, when the receiving antenna 12 with long-distance receiving capacity is used, the chance of simultaneously receiving external RF signals will relatively increase. In case a nearby vehicle is provided with wireless tire pressure sensors of similar bandwidth, the RF signals from the nearby vehicle will be received by the receiving antenna 12 of the wireless tire pressure monitoring system 1 and the monitoring main unit 10 will process these external signals, increasing the chance of error reading and packet collision. To solve this problem, an application of a complicated high-level software processing data packet can be used in the tire pressure sensors 13 and the monitoring main unit 10 to increase the ability of packet verification so as to further lower the chance of error reading; however, if this solution is adopted, the accompanying amplification of noises may interfere with effective radio signals, raising the bit error rate.